RMS Courant Number

SERVIGNAF · December 20, 2010, 16:36

hi...how to calculate the RMS courant number.....is (velocity*deltaT)/element size?? in my project I have a courant number values equal to 999.99, where this affects the solution to my problem? and how I can do to lower that value?

Thanks...

ghorrocks · December 20, 2010, 18:04

The documentation describes the calculation of Courant number.

Don't get too excited about the Courant Number. Do a time step sensitivity check instead to give you the time step your model can run at.

To lower Courant number you run a smaller time step.

SERVIGNAF · December 21, 2010, 08:30

THANKS. But I still doubt, do not know if it is conceptual, I need to see the cooling behavior of a solid body by convection, for about 10 hours, then if I use this time as total transient simulation, it appears a number of high courant. Will need to divide this time segment? or just change the steps of time?

Josh · December 21, 2010, 17:07

I like the adaptive time scheme. Set a reasonable residual value (you'll have to determine what this is) and the program will lower or raise the timestep size based on the convergence speed. It will give you an approximately appropriate timestep size.

December 20, 2010, 16:36	RMS Courant Number	#1
SERVIGNAF New Member FRANCISCO SERVIGNA Join Date: Sep 2010 Posts: 3 Rep Power: 16	hi...how to calculate the RMS courant number.....is (velocity*deltaT)/element size?? in my project I have a courant number values equal to 999.99, where this affects the solution to my problem? and how I can do to lower that value? Thanks...

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December 20, 2010, 18:04		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	The documentation describes the calculation of Courant number. Don't get too excited about the Courant Number. Do a time step sensitivity check instead to give you the time step your model can run at. To lower Courant number you run a smaller time step.

December 21, 2010, 08:30		#3
SERVIGNAF New Member FRANCISCO SERVIGNA Join Date: Sep 2010 Posts: 3 Rep Power: 16	THANKS. But I still doubt, do not know if it is conceptual, I need to see the cooling behavior of a solid body by convection, for about 10 hours, then if I use this time as total transient simulation, it appears a number of high courant. Will need to divide this time segment? or just change the steps of time?

December 21, 2010, 17:07		#4
Josh Senior Member Joshua Counsil Join Date: Jul 2009 Location: Halifax, Nova Scotia, Canada Posts: 366 Rep Power: 18	I like the adaptive time scheme. Set a reasonable residual value (you'll have to determine what this is) and the program will lower or raise the timestep size based on the convergence speed. It will give you an approximately appropriate timestep size.